Generally, battery-units in which plural batteries (battery cells) are connected together in series are employed as high capacity, high output battery-units employed for, for example, driving the motors of hybrid automobiles and electric automobiles. Specific examples of such battery-units include lithium ion battery-units. A battery monitoring system is known that monitors and controls the battery voltages of batteries in a battery-unit.
Conventional battery monitoring systems include a battery cell group having plural battery cells, and a semiconductor circuit that measure and controls the voltages of the battery cells included in the battery cell group.
In such battery monitoring systems, for example, processing to equalize cell voltages in a battery cell group (to make the voltage values of the respective battery cells equal) or processing to control charging and discharging (to control charging and discharging of the respective battery cells) is performed based on the voltage information for each battery cell obtained from a semiconductor circuit for performing measurements. In such battery monitoring systems, irregularities sometimes occur in the battery monitoring system when a line-breakage arises in, for example, a signal line connecting a battery cell to the semiconductor circuit for performing measurements.
Therefore, technology is known that detects line-breakages in signal lines (see Japanese Patent Application Laid-Open (JP-A) Nos. 2002-343445, 2001-116776, 2006-29923, 2004-170335, 2005-168118, 2004-104989, 2006-50784, 2007-225484, and 2008-175804). In particular, JP-A No. 2008-175804 describes technology that detects line-breakages in signal lines in a battery monitoring system provided with a discharging circuit for discharging the charge of battery cells.